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One manifestation of adaptive compensation is the elevated parathyroid production that occurs when vitamin D status is low. Vitamin D–mediated intestinal calcium absorption reduces parathyroid activity, and the point at which vitamin D ceases to be a limiting factor in calcium absorption is the point at which parathyroid hormone concentrations are lowest. That occurs when serum concentrations of 25(OH)D are in the range of 48–52 ng/mL [74]74.
Ginde AA, Wolfe P, Camargo CA Jr, Schwartz RS: Defining vitamin D status by secondary hyperparathyroidism in the US population. J Endocrinol Invest 35:42–48, 2012. [PubMed], [Web of Science ®] View all references. | |||||
Approximating the vitamin D status of ancestral humans, as noted above, has been done for 2 African tribes. Their average 25(OH)D concentrations (around 46 ng/mL) [26]26.
Luxwolda MF, Kuipers RS, Kema IP, Dijck-Brouwer DA, Muskiet FA: Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l. Br J Nutr 108:1557–1561, 2012. [CrossRef], [PubMed], [Web of Science ®] View all references provide the best available estimate of the level to which human physiology has been fine-tuned by natural selection over the millennia of human evolution. | |||||
A critical function of vitamin D is passage of the nutrient from mother to child in breast milk. In order to fully support the infant's need for vitamin D, the mother must have a blood concentration of cholecalciferol (vitamin D3) above 10 ng/mL, which happens only when serum 25(OH)D is above 48 ng/mL [75]75.
Hollis BW, Pittard WB III, Reinhardt TA: Relationships among vitamin D, 25-hydroxyvitaminD, and vitamin D–binding protein concentrations in the plasma and milk of human subjects. J Clin Endocrinol Metab 62:41–44, 1986. [CrossRef], [PubMed], [Web of Science ®] View all references. At today's prevailing vitamin D status values, no D3 is transferred into breast milk. Hence, currently recommended 25(OH)D concentrations are not adequate to support this critical physiological function. | |||||